The present invention relates to memory devices. In particular, the present invention relates to non-volatile memory storage.
Computer systems generally include two types of memory, volatile and non-volatile. Volatile memory is maintained in a state using electrical current. When the computer system is powered down, the data stored in volatile memory is lost. The data stored in non-volatile memory, on the other hand, persists even after the computer system has lost power.
Examples of non-volatile memory include disc drives such as magnetic and optical disc drives as well as tape drives and core memory.
In magnetic disc drives and core memory, data is stored by setting the magnetic polarity of a magnetic material. In disc drives, the magnetic polarities of small domain areas on the disc are set by a write head as it moves over the surface of the disc. To read the data from the disc, a read head moves over the disc and senses transitions in the magnetic polarity. Note that the read head must move relative to the disc in order to read the data because the read head detects the transitions in the magnetic polarity, and not the magnetic polarity itself.
The required movement of the head relative to the disc means that the disc drive must include a motor and other moving mechanical pieces. These moving pieces are difficult to control and can cause reading errors. In addition, these moving pieces are the most likely pieces to fail in a disc drive.
In core memory, an array of magnetic toroids or rings is provided. Two address wires, one a row address line and the other a column address line, pass through each ring, together with a read sensing wire. To write to a particular toroid, current is applied to the row and column address lines associated with that toroid. In particular, one half of the current needed to change the polarity of the magnetic field in the toroid is applied to each line. Thus only the toroid at the intersection of the two lines is affected by the write event. To read data from a toroid, a write signal is applied to the row and column address lines for the toroid. If this write event causes a change in the magnetic polarity of the toroid, an electric field will be generated in the read sense line. If the write event does not cause a change in the magnetic polarity of the toroid, there will be no voltage pulse on the read sense line. Thus, by monitoring the voltage on the read sense line during the write event, it is possible to read the values stored in the toroid. Note that the read is destructive since it writes to the toroid. Because of this, the toroid must be rewritten to reestablish its value after the data has been read.
In core memory, a single sense line is provided for all of the toroid cells. Because of this, when a voltage is induced on the sense line by the switching of a cell, the voltage can become dampened as it interacts with the other toroid cells. In addition, it is impossible to tell whether a voltage detected on the sense line is due to the toroid cell that is currently being addressed or is due to some other toroid cell that has experienced a thermal event which caused its magnetic polarity to flip.
Thus, a non-volatile storage system is needed that does not require moving parts and that does not require a separate sense line.
Embodiments of the present invention provide a solution to these and other problems, and offer other advantages over the prior art.
A method and apparatus are provided for storing and retrieving data in a non-volatile manner. The data is stored in a magnetic cell having a magnetic moment with a direction. A conductor passes around an arm of the cell and carries a current formed by a current driver. A data detector detects a value for data stored in the cell based on a level of current driven through the conductor.
These and various other features as well as advantages which characterize the invention will be apparent upon reading of the following detailed description and review of the associated drawings.